Magnetic compass

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Image
The magnetic compass is fitted on the upper bridge exactly center line of the ship   It is referred to as standard compass     1. D ry C ard    2. W et C ard   A compass point north because all magnets have two poles north pole, south pole.   The north pole of the one magnet attracted towards the south pole of another magnet     DRY CARD COMPASS   A light aluminum ring about 254mm in diameter is attached to a brass hub by silk cord which is threaded in and out through holes in the ring.   This tight silk cord is act like bicycle wheels.   There is no other connection or support between the ring and the hub.   Silk cord is used because it doesn’t shrink or stretch due to moisture or change in atmospheric temperature.     Card support: -     The bottom of the hub has small cap fi tt ed with a sapphire bearing surface.   This rests on a pivot tipped with iridium which is hard nonmagnetic metal....
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Double bottom

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DOUBLE BOTTOM

#All ocean going ships with the exceptions of tankers,and most coastal vessels are fitted with a double bottom which extends from fore to aft .


#A double bottom tank is formed by introducing a plate on top of the bottom keel plate.the height of the double bottom tank is 1 to 1.5 metres.


#This double bottom forms extra stability and extra protection to the hull.


#It is used for carrying ballast,freshwater, fuel oil.structurally double bottom tanks are divided longitudinally as well as transversely into very big tanks which allows different liquids to be carried and may be used to correct the heel of a ship or to change the trim.


#access to these tanks are arranged in the form of manhole with watertight doors.


#also the double bottom gives extra longitudinal strength to the bottom of the ship where this is most required. as the mass of the cargo acts on the bottom ,this area needs to be the strongest especially when carrying high density cargoes.



#Because of their location, double bottoms help to maintain safe levels of stability(gm) during ballast passages while providing the required draughts and trim.


#since most of the double bottoms are longitudinally divided free surface effect due to the slack tanks being reduced to negligible levels.


*in construction wise two types of double bottoms are there


1.transversely framed double bottom

2.longitudinally framed double bottom.













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Magnetic compass

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